An open end wrench is a wrench that has an open ended wrench head used to turn and control the rotation of bolts, nuts and various fasteners. Examples of open end wrenches include, but are not limited to, double open end, combination, flare nut, flex head etc. An open end wrench can access fasteners under certain limited-access conditions where a closed end or box wrench cannot, however, an open end wrench is much weaker by design than a box wrench. The weakness is associated with the inevitable jaw expansion of the wrench produced by the cam effect of fastener to wrench, under torque. This inherent weakness reduces torque capacity and promotes fastener deformation and wrench wear.
Subsequently, there have been numerous attempts to increase the strength and torque capacity of open end wrenches. The use of sharp teeth or serrations has been relatively effective on all but extremely hard fasteners, however, this technology sacrificed the fastener to gain additional torque by leaving bite or shred marks on the fastener. The use of inclined and arcuate driving surfaces has been effective at reducing the bite marks and fastener deformation, however, this technology has been generally less effective at increasing wrench strength and torque capacity. In addition, most prior attempts to improve the torque capacity of open end wrenches have consequently produced an increase in the total free play arc between wrench and fastener which applicant believes to be objectionable to most users.